WAVE-FRONT ANALYSIS WITH HIGH-ACCURACY BY USE OF A DOUBLE-GRATING LATERAL SHEARING INTERFEROMETER

A phase-stepped double-grating lateral shearing interferometer to be u sed for wave-front analysis is presented. The resulting interference p atterns are analyzed with a differential Zernike polynomial matrix-inv ersion method. Possible error sources are analyzed in the design stage , and it is shown that the inaccuracy can be kept within 2-5 m lambda rms. The apparatus was tested and evaluated in practice. Comparison wi th a phase-stepped Twyman-Green interferometer demonstrates that the a ccuracy of the two methods is comparable. Lateral shearing interferome try scores better on reproducibility, owing to the stability and robus tness of the method. (C) 1996 Optical Society of America